JPS6357375A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To suppress an increase of an understeering tendency by setting the specific change characteristic of the steering ratio so that the steering state of front wheels and the steering state of rear wheels are in the same phase relationship from the low-vehicle speed condition and the travel stability is large when the engine start is detected. CONSTITUTION:A rear wheel steering mechanism interlocked with the steering of front wheels has a pulse motor 30 moving a rear wheel steering rod and a pump drive motor 44 applying a hydraulic assist force and is controlled by a control unit 50. In this case, the control unit 50 is constituted of a steering ratio characteristic selecting unit 59 selecting one of multiple steering ratio characteristics stored in a memory unit 58 based on the detected value of a lateral force and a rear wheel steering angle arithmetic unit 60 calculating the rear wheel steering angle based on the steering ratio characteristic and the detected values of the steering angle and the vehicle speed. A steering ratio characteristic specifying unit 57 is provided which sets the specific steering ratio so that the steering state of front wheels and the steering state of rear wheels are in the same phase relationship from the low-vehicle speed condition and the travel stability is large when the engine start is detected by an engine start sensor 55.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a four-wheel drive system of a vehicle in which when the front wheels are steered by a steering operation via a steering wheel, the rear wheels are also steered at the same time. It relates to a wheel steering device.

(Prior art) When the front wheels are steered by a steering operation performed through the steering wheel, the rear wheels are also steered as the front wheels are steered, thereby preventing side slip of the rear wheels. As a four-wheel steering system that improves vehicle drivability by steering the vehicle in a reduced state, the ratio of the steering angle of the rear wheels to the steering angle of the front wheels, that is, the steering It is known that the steering ratio has a vehicle speed-sensitive steering ratio characteristic in which the ratio is changed depending on the vehicle speed.

In a four-wheel steering system having such a vehicle speed-sensitive steering ratio characteristic, when the vehicle is traveling at a relatively low speed, the front wheel steering state and the rear wheel steering state usually have an opposite phase relationship. When the vehicle is running at a relatively high speed, the front wheel steering state and the rear wheel steering state are assumed to have the same phase relationship. The steering ratio is set.

When the steering ratio is set so that the front wheel steering state and the rear wheel steering state are in an opposite phase relationship, the vehicle tends to oversteer, and the turning performance is improved. When the steering ratio is such that the front wheel steering state and the rear wheel steering state have the same phase relationship, the vehicle tends to understeer,
Driving stability is improved.

For example, as described in Japanese Unexamined Patent Publication No. 60-135368, a steering ratio that changes depending on the vehicle speed is used to enable the vehicle to take on a plurality of driving modes according to the driver's wishes. A four-wheel steering system has been proposed in which a plurality of characteristics are set in advance, and a steering ratio characteristic can be arbitrarily selected by manual operation by a driver or the like. In such a four-wheel steering device, for example, a selection switch for selecting an arbitrary one from among a plurality of steering ratio characteristics is arranged, and the selection switch is operated by the driver etc. to change the steering ratio. By arbitrarily selecting a steering ratio characteristic and steering the rear wheels according to the selected steering ratio characteristic, a vehicle running state corresponding to the driving mode desired by the driver can be obtained.

(Problems to be Solved by the Invention) However, as described above, a plurality of steering ratio characteristics are set in advance, and the steering ratio characteristics are arbitrarily selected by the driver's manual operation. In wheel steering devices,
the selection switch remains in a predetermined operating position that specifies a particular steering ratio characteristic, and therefore the rear wheels are steered in accordance with the particular steering ratio characteristic; There are cases where the engine is stopped and the vehicle is put into a non-driving state, and then the vehicle is put into a running state again. In such a case, the rear wheels of the vehicle are steered according to a specific steering ratio characteristic based on the operating position of the selection switch from the initial running of the vehicle. For this reason, for example, when the selection switch is in the operating position that specifies the steering ratio where the front wheel steering state and the rear wheel steering state have an opposite phase relationship when the vehicle is running, Even in conditions where the friction coefficient of the road surface is relatively small, such as during snowfall, the vehicle may be subject to an undesirable oversteering tendency.

In view of this, the present invention provides a system in which the characteristic of the ratio of the steering angle of the rear wheels to the steering angle of the front wheels, which is changed according to the vehicle speed, that is, the steering ratio characteristic, can be arbitrarily changed by manual operation. An object of the present invention is to provide a four-wheel steering device for a vehicle that can reduce the situation in which the vehicle is subjected to an undesirable oversteering tendency when the vehicle is driven by a vehicle and the coefficient of friction of the road surface is relatively small. .

(Means for Solving the Problems) In order to achieve the above-mentioned object, a four-wheel steering device for a vehicle according to the present invention includes a front wheel steering mechanism that steers the front wheels in response to a steering operation, and a front wheel steering mechanism that steers the front wheels in response to a steering operation. a rear wheel steering mechanism that steers the rear wheels according to the steering angle; a steering ratio control means that manually changes the change characteristic of the ratio of the steering angle of the rear wheels to the steering angle of the front wheels; and starting of an engine installed in the vehicle. and a steering ratio characteristic specifying means. The change characteristic of the ratio of the steering angle of the rear wheels to the steering angle of the front wheels, which is controlled by the means, is forcibly changed from a state where the running speed of the vehicle is relatively low to a state where the front wheels are steered and a state where the rear wheels are steered. It is assumed that the phase relation is the same and that the running stability of the vehicle is increased.

(Function) In the four-wheel steering system for a vehicle according to the present invention configured as described above, when the front wheels are steered by the front wheel steering mechanism, the rear wheel steering mechanism turns the rear wheels along with the steering of the front wheels. The wheels are steered, and at this time, the steering ratio control means
Change characteristics of the ratio of the rear wheel steering angle to the front wheel steering angle, that is,
The steering ratio characteristic is changed by manual operation. Then, when the engine start detecting means detects that the engine has started, the steering ratio characteristic specifying means forcibly changes the steering ratio characteristic from a relatively low running speed of the vehicle to a state in which the front wheels are turned. This is a specific condition in which the steering condition and the steering condition of the P wheels are in the same phase relationship, thereby increasing the running stability of the vehicle.

By doing this, when starting the engine,
The steering ratio characteristic is forced to be a specific one in which the front wheel steering state and the rear wheel steering state are in the same phase relationship from a state where the vehicle travel speed is relatively low, and this As a result, the running stability of the vehicle is said to be improved, so that, for example, when the friction coefficient of the road surface is relatively small, the situation where the vehicle tends to undesirably oversteer is significantly reduced. Become.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 schematically shows an example of a four-wheel steering system for a vehicle according to the present invention. In Figure 1, left and right front wheels 2L and 2
A front wheel steering mechanism 5 is provided to steer the wheel R in response to steering via the steering wheel 3. A pair of knuckle members 6 supported by the vehicle body (not shown) via. A rank shaft having a pair of tie rods 8 each having one end connected to the knuckle arms 6a of these knuckle members 6, and a rank shaft 9 having the other ends of each of the pair of tie rods 8 connected to both ends thereof. It is comprised of a steering gear mechanism 10 that is of an and-pinion type.

In such a front wheel steering mechanism 5, the steering force from the steering wheel 3 is transmitted to the tie rod 8 by the steering gear mechanism 10, and the tie rod 8 reciprocates in the vehicle width direction. As a result, the knuckle member 6 is rotated around the joint portion 4, and the front wheels 2L and 2R are steered.

Also, replace the left and right rear wheels 12L and 12R with the front wheels 2L and 2
A rear wheel steering mechanism 11 is provided which steers the wheels in accordance with each steering of the rear wheels 12L.
A pair of knuckle members 16 which rotatably support and 12R and are supported by a vehicle body (not shown) via a joint portion 14, and a pair of tie rods 1 each having one end connected to a knuckle arm 16a of the knuckle member 16.
8, and a rear wheel steering rod 20, the other end of each of which is connected to both ends of the pair of tie rods 18. A rank 22 is formed on the rear wheel steering rod 20,
The rack 22 is meshed with a pinion 26 fixed to one end of a pinion shaft 24. A bevel gear 28 is fixed to the other end of the pinion shaft 24, and the bevel gear 28 is a bevel gear 3 fixed to the output shaft of the pulse motor 30.
2 is engaged. In such a rear wheel steering mechanism 11, the driving force of the pulse motor 30 is transmitted to the pinion shaft 24 via the bevel gears 32 and 28.
The rear wheel steering rod 20 is moved along the vehicle width direction in accordance with the rotation direction and rotation time of the pulse motor 30.

Furthermore, a power cylinder 34 is arranged in relation to the rear wheel steering rod 20. The power cylinder 34 has a piston 34a fixed to the rear wheel steering loft 20 and hydraulic chambers 34b and 34c partitioned by the piston 34a. The hydraulic chambers 34b and 34c communicate with a control valve 38 through hydraulic passages 36 and 37, respectively.

The control valve 38 is communicated with a hydraulic pump 42 via an oil supply passage 40 and an oil return passage 41, and the hydraulic pump 42 is rotationally driven by a pump driving motor 44.

The control valve 38 controls the hydraulic chambers 34b and 34 of the power cylinder 34 depending on the rotational direction of the pinion shaft 24.
For example, when the rear wheels 12L and 12R are steered clockwise in FIG. Pressure oil from the pump 42 is supplied into the hydraulic chamber 34b, and the oil return passage 41 and the hydraulic passage 37 are brought into communication, so that the pressure oil in the hydraulic chamber 34C is returned to the hydraulic pump 42. Further, when the rear wheels 12L and 12R are steered counterclockwise in FIG. 1, the oil supply passage 40 and the hydraulic passage 37 are brought into communication, and pressure oil from the hydraulic pump 42 is supplied into the hydraulic chamber 34C. In addition, the oil return passage 41 and the hydraulic passage 36 are communicated with each other, so that the pressure oil in the hydraulic chamber 34b is transferred to the hydraulic pump 42.
will be returned to. In this way, the driving force of the pulse motor 30 is transmitted to the pinion shaft 24 via the bevel gears 32 and 28, so that when the rear wheel steering rod 20 is moved in the vehicle width direction, the power cylinder 34 is Hydraulic chamber 3
Pressure oil is supplied and discharged to and from the rear wheels 4b and 34c, thereby assisting the movement of the rear wheel steering rod 20 in the vehicle width direction, and steering the rear wheels 12L and 12R.

The pulse motor 30 and the pump drive motor 44 receive drive signals Sa and s sent from the control unit 50, respectively.
The drive is controlled by b. The control unit 50 receives a detection signal Ss from a steering angle sensor 52 that detects the steering angles of the front wheels 2L and 2R in relation to the front wheel steering mechanism 5, and a vehicle speed based on the rotation speed of the wheel (in this example, the left front wheel 2L). a detection signal 3v from a vehicle speed sensor 54 that detects the start of the engine, and an engine start sensor 5 that detects that the engine (not shown) has started.
A detection signal Se from 5 and a signal sh from a steering ratio characteristic designation switch 56 for specifying an arbitrary steering ratio characteristic by manual operation by a driver or the like are supplied.

The control unit 50 has, for example, a specific configuration as shown in FIG. The signal Sh is received from among the plurality of steering ratio characteristics stored in the steering ratio characteristic storage section 58.
A steering ratio characteristic selection unit 59 selects an arbitrary steering ratio characteristic designated by the driver or the like and sends out a signal Sk corresponding to the selected steering ratio characteristic, and the engine start sensor 55 detects this. When the signal Se is supplied, the steering ratio characteristic selection section 59 selects one of the plurality of steering ratio characteristics stored in the steering ratio characteristic storage section 58 that provides the highest running stability of the vehicle. A steering ratio characteristic specifying section 57 that supplies a signal SZ to select a specific one; a steering ratio characteristic selecting section that receives a detection signal Ss from the steering angle sensor 52 and a detection signal Sv from the vehicle speed sensor 54; Upon receiving the signal Sk indicating the steering ratio characteristics from 59, a calculation is performed to calculate the front wheel steering angle and the rear wheel steering angle according to the vehicle speed based on the signals, and the calculation is performed according to the calculated rear wheel steering angle. a rear wheel steering angle calculating section 60 that sends out a signal Sr; a pulse signal forming section 61 that forms a pulse signal Sp based on the signal Sr from the rear wheel steering angle calculating section 60;
Based on the pulse signal Sp obtained from the pulse signal forming section 61, the pulse motor 30 and the pump drive motor 44
and a drive section 62 that sends out drive signals Sa and sb for the drive signals Sa and sb. Here, the rear wheel steering angle calculating section 60 in the control unit 50. The front wheel 2L is controlled by the pulse signal forming section 61, the driving section 62, the pulse motor 30, etc.
A steering ratio control means is configured to control the steering ratio obtained by the ratio of the steering angles of the rear wheels 12L and 12R to the steering angle of the rear wheels 12L and 2R. When the detection signal Se indicating that the engine has started is supplied from 55, the steering ratio changed by the steering ratio control means is changed between the steering state of the front wheels 2L and 2R and the steering state of the rear wheels 12L and 12R. A steering ratio characteristic specifying means is provided for determining a specific state such that the state has the same phase relationship even from a state where the vehicle speed is relatively low, thereby increasing the running stability of the vehicle.

The steering ratio characteristics stored in the steering ratio characteristics storage section 58 are as follows:
For example, as shown in the graph of FIG. 3, where the vertical axis represents the steering ratio K and the horizontal axis represents the vehicle speed V, the steering angle is determined when the friction coefficient of the road surface is relatively small. 1 for rudder ratio characteristics
．． The steering ratio characteristic taken when the friction coefficient of the road surface is relatively large is 2°, and the steering ratio characteristic taken when the road surface friction coefficient is large is 3, compared to the case where the steering ratio characteristic kt is taken. The steering ratio characteristics are roughly divided into four types, which are obtained when the coefficient of friction of the road surface is larger than when the steering ratio characteristics are obtained. These steering ratio characteristics, , 2, and 4 are respectively when the vehicle speed is less than V, , Vt is greater than V, ■3 is greater than V, 1 is greater, and ■ V4 is greater than 3. Steering ratio K
takes a negative value, that is, the steering state of the front wheels 2L and 2R and the steering state of the rear wheels 12L and 12R are in an opposite phase relationship, and the vehicle speed is Vt, Vt, Vs and 74 or higher. When the steering ratio K takes a positive value, that is,
The steering state of the front wheels 2L and 2R and the steering state of the rear wheels 12L and 12R are made to have the same phase relationship. Furthermore, the steering ratio characteristic k.

, , , and 4 respectively, the value of the steering ratio increases as the vehicle speed increases, and also takes a common negative value at low vehicle speeds and takes a common negative value at high vehicle speeds. are set to take a common positive value.

Then, the steering ratio characteristic is 2, compared to the steering ratio characteristic,
The steering ratio K is the steering state of the front wheels 2L and 2R and the rear wheel 12L.
The steering state of 12R and 12R are shifted to the opposite phase side, and the steering ratio K is compared to 2. The steering state of the front wheels 2L and 2R and the steering state of the rear wheels 12L and 12R have shifted to the opposite phase side, which means that the steering state of the rear wheels 12L and 12R is in an opposite phase relationship. In terms of characteristics, compared to
The relationship is such that the steering state is shifted to the opposite phase side.

When the vehicle is started to run based on the above-described configuration, first, a detection signal Se indicating that the engine has started is sent from the engine start sensor 55 to the steering ratio characteristic specifying section 57 of the control unit 50. A signal SZ is supplied from the steering ratio characteristic specifying section 57 to the steering ratio characteristic selecting section 59. Then, the steering ratio characteristic selection unit 59 selects the steering ratio characteristic shown in FIG. 3 from among the plurality of steering ratio characteristics stored in the steering ratio characteristic storage unit 58.
A signal Sk corresponding to 1 in the steering ratio characteristic is sent to the rear wheel steering angle calculation unit 60.
supplied to Thereby, in the rear wheel steering angle calculating section 60, the detection signal SV from the vehicle speed sensor 54 is the actual vehicle speed, the signal Sk is the actual steering ratio characteristic, and the steering ratio K and the steering angle obtained from The rear wheel steering angle corresponding to the vehicle speed at which the detection signal SV is generated is calculated from the front wheel steering angle at which the detection signal Ss from the sensor 52 is generated, and the signal Sr corresponding to the obtained rear wheel steering angle is sent to the pulse signal forming section. 61.

Then, in the pulse signal forming section 61, a pulse signal Sp corresponding to the rear wheel steering angle indicated by the signal Sr is formed and supplied to the drive section 62.
Drive signals Sa and Sb based on the above are generated and supplied to the pulse motor 3o and the pump drive motor 44, respectively. As a result, the pulse motor 30 and the pump drive motor 44 are driven according to the rear wheel steering angle calculated by the rear wheel steering angle calculating section 60.

In this way, by driving and controlling the pulse motor 30 and the pump drive motor 44, the rear wheels 12L and 12R are steered according to the steering ratio characteristics, and when the vehicle runs at a speed less than 71, the rear wheels 12L and 12R are steered according to the steering ratio characteristics. , front wheels 2L and 2
The steering state of R and the steering state of rear wheels 12L and 12R are in an opposite phase relationship, and good turning performance is obtained.
When the vehicle runs at a vehicle speed of 71 or more, the steered states of the front wheels 2L and 2R and the steered states of the rear wheels 12L and 12R are in the same phase relationship, resulting in a stable running state.

When the vehicle travels with the rear wheels 12L and 12R being steered according to the steering ratio characteristic 1, when the steering ratio characteristic designation switch 56 is operated by the driver or the like, the steering ratio characteristic The selection unit 59 selects a steering ratio characteristic k other than the steering ratio characteristic stored in the steering ratio characteristic storage unit 58.
At t-, the one designated by the signal sh is selected from among the four. Then, a signal Sk corresponding to the selected steering ratio characteristic, , or 4 is supplied from the steering ratio characteristic selection section 59 to the rear wheel steering angle calculation section 60 .

As a result, in the rear wheel steering angle calculating section 60, the detection signal Sv from the vehicle speed sensor 54 corresponds to the actual vehicle speed and the signal Sk corresponds to the actual steering ratio characteristic. or 4, and the detection signal S from the steering angle sensor 52.
From the front wheel steering angle at which s occurs, a rear wheel steering angle corresponding to the vehicle speed at which the detection signal Sv causes a hail is calculated, and a signal Sr corresponding to the obtained rear wheel steering angle is supplied to the pulse signal forming section 61 . Also in this case, the pulse signal Sp corresponding to the rear wheel steering angle indicated by the signal Sr is supplied from the pulse signal forming section 61 to the drive section 62, and the drive signal Sa and the drive signal Sa based on the pulse signal Sp are supplied from the drive section 62. sb is supplied to the pulse motor 30 and the pump drive motor 44, respectively, and the pulse motor 3
0 and the rear wheel steering angle calculation unit 6o of the pump drive motor 44.
Drive is performed according to the rear wheel steering angle calculated in .

By controlling the drive of the pulse motor 3o and the pump drive motor 44 in this manner, the rear wheels 12L and 12R have the steering ratio characteristic .k.

Or the vehicle is steered according to 4, and the vehicle speed is V,
, V, or when driving at less than 71, the front wheel 2L
And the steering state of 2R and the steering state of rear wheels 12L and 12R are placed in an opposite phase relationship, and good turning performance is obtained.
In addition, when the vehicle runs at a vehicle speed of v2, ■3 or 74 or higher, the steering state of the front wheels 2L and 2R and the rear wheel 12L
and the steering state of 12R are placed in the same phase relationship, resulting in a stable running state.

In this case, the steering ratio characteristics, , and 4 are such that the steering ratio K is different from the steering condition of the front wheels 2L and 2R and the steering condition of the rear wheels 12L and 12R. The steering state of the front wheels 2L and 2R is assumed to have shifted to the opposite phase side where the steering state is in an opposite phase relationship, and the steering state of the front wheels 2L and 2R remains unchanged until the vehicle speed reaches ■, larger V, , V, and V4. and rear wheels 12L and 12R
The state in which the steering state is in an antiphase relationship with the steering state is maintained.

Therefore, good turning performance can be obtained not only when the vehicle is running at a relatively low speed but also when the vehicle is running at a relatively high speed.

For example, while the steering ratio characteristic designation switch 56 is kept in a predetermined operating position that specifies 3 or 4 as the steering ratio characteristic, the steering The engine is stopped and the vehicle is put into a non-running state while the rear wheels 12L and 12R are steered according to the specific characteristic kt, or according to the specific characteristic kt, and then the vehicle is put into a running state again. In this case, first, a detection signal Se indicating that the engine has started is supplied from the engine start sensor 55 to the steering ratio characteristic specifying section 57 of the control unit 50, and the steering ratio characteristic specifying section 57 outputs a detection signal Se indicating that the engine has started. A signal sl is supplied to the ratio characteristic selection section 59.

As a result, the steering ratio characteristic selection section 59 selects the steering ratio characteristic storage section regardless of whether the steering ratio characteristic specified according to the operation position of the steering ratio characteristic designation switch 56 is set to , , or 4. 58 is selected as the steering ratio characteristic shown in FIG.
A signal Sk corresponding to the rear wheel steering angle calculation section 60 is supplied to the rear wheel steering angle calculation section 60.

As a result, the rear wheels 12L and 12R have steering ratio characteristics,
Therefore, even when the vehicle speed is relatively low, the steering state of the front wheels 2L and 2R and the rear wheel 12
Since the steering states of L and 12R are in the same phase relationship, a stable running state can be obtained.

By doing so, the steering ratio characteristic specification switch 56 specifies a specific steering ratio in which the steering state of the front wheels 2L and 2R and the steering state of the rear wheels 12L and 12R are in an opposite phase relationship. Even when the vehicle is running on a road surface where the coefficient of friction is relatively small during rain or snow, while the vehicle is in a predetermined operating position, The situation in which the vehicle tends to undesirably oversteer is significantly reduced, and the running stability of the vehicle is improved.

FIG. 4 shows another specific example of the configuration of the control unit 50 used in the embodiment shown in FIG.

The specific configuration example shown in FIG. 4 includes, for example, a steering ratio characteristic storage section 58'' that stores only 1 in the steering ratio characteristic shown in FIG. The detection signal Sv from the vehicle speed sensor 54 is supplied, and the rear wheel steering angle is calculated based on the detected front wheel steering angle and vehicle speed, and the steering ratio characteristic stored in the steering ratio characteristic storage section 58. A signal S corresponding to the calculated rear wheel steering angle is calculated.
A signal sh is supplied from the rear wheel steering angle calculation unit 60 which sends out r, and the steering ratio characteristic designation switch 56, and the signal sh is used to adjust the rear wheel steering angle according to an arbitrary steering ratio characteristic specified by the driver or the like. A correction unit 65 corrects the rear wheel steering angle calculated by the wheel steering angle calculation unit 60 and sends out a signal Sr' corresponding to the rear wheel steering angle after the necessary correction, and a detection signal Se from the engine start sensor 55. a steering ratio characteristic specifying section 57' that supplies a signal SR to the correction section 65 when the signal Sr is supplied, and sends out the signal Sr from the rear wheel steering angle calculation section 60 as is as a signal Sr" from the correction section 65; and a correction section. A pulse signal forming section 61 forms a pulse signal Sp corresponding to the signal Sr° from the pulse signal forming section 65, and a drive signal for the pulse motor 30 and the pump driving motor 44 is generated based on the pulse signal Sp obtained by the pulse signal forming section 61. It is equipped with a drive unit 62 that sends out Sa and sb.

When the vehicle is started to run under such a configuration, first, a detection signal Se indicating that the engine has started is sent from the engine start sensor 55 to the control unit 5.
0 to the steering ratio characteristic specifying section 57°, and the signal SN is supplied from the steering ratio characteristic specifying section 57° to the correcting section 65. In addition, in the rear wheel steering angle calculating section 60, the detection signal Sv from the vehicle speed sensor 54 is stored in the vehicle speed and steering ratio characteristic storage section 5.
8', the steering ratio K obtained from The rear wheel steering angle is calculated, and a signal S corresponding to the obtained rear wheel steering angle is generated.
r is supplied to the correction section 65.

In this way, the detection signal Se from the engine starting sensor 55
is obtained, a signal S7! is sent from the steering ratio characteristic specifying section 57' to the correcting section 65! is supplied, the correction unit 65 does not correct the rear wheel steering angle caused by the signal Sr from the rear wheel steering angle calculation unit 60. Therefore, the correction unit 65
The signal Sr from the rear wheel steering angle calculation unit 60 is the signal Sr as it is.
' and is supplied to the pulse signal forming section 61.

Then, in the pulse signal forming section 61, a pulse signal Sp corresponding to the rear wheel steering angle indicated by the signal Sr° is formed and supplied to the drive section 62.
Drive signals Sa and sb based on p are generated and supplied to the pulse motor 30 and the pump drive motor 44, respectively. As a result, the pulse motor 30 and the pump drive motor 44 are driven according to the rear wheel steering angle calculated by the rear wheel steering angle calculating section 60.

In this way, by controlling the drive of the pulse motor 30 and the pump drive motor 44, the rear wheels 12L and 12R are steered in accordance with the steering ratio characteristics, as shown in FIG. The same running state of the vehicle as in the case of the configuration example can be obtained.

Further, the rear wheels 12L and 12R have a steering ratio characteristic k.

When the vehicle is running in a state where it is steered according to
When the steering ratio characteristic designation switch 56 is operated by the driver or the like and the signal sh is supplied to the correction section 65, the correction section 65 receives the signal Sr from the rear wheel steering angle calculation section 60 to adjust the steering ratio characteristics to the rear wheels. Correction is made to the steering angle, and for example, in the rear wheel steering angle calculating section 60, instead of the steering ratio characteristic, , or 4 is used for the steering ratio characteristic shown in FIG. 3. is performed, a corrected rear wheel steering angle is obtained which corresponds to the rear wheel steering angle calculated at that time. Then, the correction section 65 supplies a signal Sr' corresponding to the corrected rear wheel steering angle to the pulse signal formation section 61. Also in this case, the pulse signal forming section 61 outputs the signal Sr.
A pulse signal Sp corresponding to the corrected rear wheel steering angle indicated by " is supplied to the drive section 62, and drive signals Sa and sb based on the pulse signal Sp are supplied from the drive section 62 to the pulse motor 30 and the pump drive motor 44, respectively. The rear wheel steering angle calculation unit 6 of the pulse motor 30 and the pump drive motor 44
Drive is performed according to the rear wheel steering angle calculated at 0.

By controlling the pulse motor 30 and the pump drive motor 44 in this way, the rear wheels 12L and 12R have a steering ratio characteristic of 2. The vehicle is steered in accordance with .times.3 or .times.4, and the same running state of the vehicle as in the specific configuration example shown in FIG. 2 described above is obtained.

For example, the steering ratio characteristic designation switch 56 remains in a predetermined operating position in which it specifies 4 or 4 depending on the steering ratio characteristic. ,, according to 3 or 4 rear wheels 12L and 1
When the engine is stopped and the vehicle is put into a non-running state while 2R is being steered, and then the vehicle is put into a running state again, the engine start sensor 55 first detects that the engine is not running. A detection signal Se indicating that the engine has started is supplied to the steering ratio characteristic specifying section 57'' of the control unit 50, and a signal Sl is supplied from the steering ratio characteristic specifying section 57' to the correction section 65. The steering ratio characteristic specified according to the operating position of the steering ratio characteristic designation switch 56,
, or 4, the correction section 65 does not correct the rear wheel steering angle when the signal Sr from the rear wheel steering angle calculation section 60 occurs. Therefore, from the correction unit 65,
The signal Sr from the rear wheel steering angle calculation unit 60 is the signal Sr as it is.
' is obtained and supplied to the pulse signal forming section 61. Then, in the pulse signal forming section 61, the signal Sr
A pulse signal Sp corresponding to the rear wheel steering angle indicated by ' is generated and supplied to the drive section 62. As a result, the rear wheels 12L and 12R are steered according to the steering ratio characteristics,
Therefore, even when the vehicle speed is relatively low, the steered state of the front wheels 2L and 2R and the steered state of the rear wheels 12L and 12R are in the same phase relationship, and a stable running state can be obtained. become.

FIG. 5 shows another example of a four-wheel steering system for a vehicle according to the present invention. In FIG. 5, parts corresponding to the example shown in FIG. 1 are given the same reference numerals as in FIG. 1. and redundant explanations thereof will be omitted.

In the example shown in FIG. 5, a rack 70 is formed on the rack shaft 9 of the steering gear mechanism 10 constituting the front wheel steering mechanism 5''. A pinion 74 fixed to one end of the loft 72 is engaged with the transmission rod 7.
The other end of 2 is connected to a steering ratio changing mechanism 76. The steering ratio changing mechanism 76 includes a slide member 78 supported movably in the vehicle width direction. A rack 80 is formed on the slide member 78, and a pinion 82 fixed to one end of the pinion shaft 24 is meshed with the rack 80. A pinion 26 is attached to the other end of the pinion shaft 24.
is fixed, and this pinion 26 is meshed with a rack 22 formed on the rear wheel steering rod 20.

For example, as shown in FIG. 6, the steering ratio changing mechanism 76 has a shaft 83 rotatably supported around a central axis 01 extending in the height direction of the vehicle, and one end of the shaft 83 A holder 84 having a bifurcated shape is attached to the portion. One end of a rotating arm 88 is connected to the holder 84 via a pin 86, and the center of the pin 86 is aligned with a central axis o2 that is perpendicular to the central axis OI and extends in the vehicle width direction. ing. Therefore, the angle of the rotation locus of the rotation arm 88 about the pin 86 with respect to the central axis 0. It changes as the holder 84 rotates around .

The other end of the rotating arm 88 is connected to the slide member 78 via a link member 92 whose intermediate portion is connected by a ball joint 90'.

The other end of the rotating arm 88 and one end of the link member 92, and the other end of the link member 92 and the slide member 78 are connected via ball joints 94 and 95 on the central axes OI and O2, respectively. has been done. Link member 92
The intermediate portions of the ball joints 90 and 94 are supported by a cylindrical member 96 so as to be slidable in the vehicle width direction. The cylindrical member 96 is fixed to the other end of a rotating arm 100, which has one end fixed to a rotating shaft 98 that is rotatably supported about the central axis 02. A bevel gear 102 is fixed to one end of the rotating shaft 98, and the bevel gear 102 meshes with a bevel gear 104 fixed to the other end of the transmission rod 72.

Therefore, the cylindrical member 96 is rotated about the rotation axis 98 by the rotation of the transmission loft 72 accompanying the operation of the front wheel steering mechanism 5'. In such a state, if the rotation locus of the rotation arm 88 is inclined with respect to the central axis 0□, the link member 92 will move in the direction of the arrow F in FIG.
This causes the slide member 78 to be displaced in the vehicle width direction.

The amount of displacement of the slide member 78 is determined by the angle between the rotation locus of the rotation arm 88 about the pin 86 and the center axis 0□, that is, the rotation angle of the holder 84 about the center axis OI. Ru. For this reason, a sector gear 106 is fixed to the other end of the shaft 83 with a holder 84 fixed to one end, and the sector gear 106 is connected to a motor 108 which is driven and controlled by a drive signal Sa from the control unit 50. A pinion 110 fixed to the output shaft is meshed with the output shaft. In this example, the rear wheel steering angle calculating section 60 in the control unit 50. The pulse signal forming section 61, the driving section 62, the steering ratio changing mechanism 76, and the like constitute a steering ratio control means.

When a vehicle equipped with the four-wheel steering device configured as described above is running, the steering force from the steering wheel 3 is transmitted to the steering ratio changing mechanism 76 via the front wheel steering mechanism 5° and the transmission rod 72. , when the control unit 50
, detection signals Ss, Sv, and Se from the steering angle sensor 52, vehicle speed sensor 54, and engine start sensor 55
s and a signal sh from the steering ratio characteristic designation switch 56
The steering ratio is set based on. A drive signal Sa corresponding to the set steering ratio is supplied from the control unit 50 to the steering ratio changing mechanism 76, thereby displacing the slide member 78 by a predetermined amount.

The displacement of the slide member 7B is transmitted to the rear wheel steering rod 20 via the binion shaft 24, and the knuckle member 1
6 is rotated around the joint portion 14, the rear wheels 12R and 12L are steered at a predetermined steering ratio.

Other configurations and operations in the embodiment shown in FIG. 5 are similar to those in the embodiment shown in FIG.

(Effects of the Invention) As is clear from the above description, according to the four-wheel steering system for a vehicle according to the present invention, the change characteristic of the ratio of the steering angle of the rear wheels to the steering angle of the front wheels is changed according to the vehicle speed. That is, the steering ratio characteristic can be arbitrarily changed by manual operation, and when the engine is started while the vehicle is running, the steering ratio is forced to change when the vehicle is running at a relatively low speed. The steering condition of the front wheels and the steering condition of the rear wheels are set to have the same phase relationship, and the running stability of the vehicle is made to be great. , when the coefficient of friction of the road surface is relatively small, the situation where the vehicle tends to undesirably oversteer is significantly reduced, driving stability is improved, and the system is adapted to the driving mode desired by the driver. Therefore, it is possible to obtain an appropriate vehicle running condition.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram schematically showing an example of a four-wheel steering system for a vehicle according to the present invention, and FIG. 2 is a block diagram showing a specific configuration example of a control unit used in the example shown in FIG.
FIG. 3 is a diagram showing steering ratio characteristics used to explain the operation of the specific configuration example of the control unit shown in FIG. 2, and FIG.
A block diagram showing another example of the specific configuration of the control unit used in the example shown in the figure, FIG.
FIG. 6 is a general configuration diagram showing another example of the wheel steering device, and FIG. 6 is a schematic configuration diagram showing a specific example of the configuration of a steering ratio changing mechanism used in the example shown in FIG. In the figure, 2L and 2R are front wheels, 5 and 5° are front wheel steering mechanisms, 11 is a rear wheel steering mechanism, 12L and 12R are rear wheels, 30
50 is a pulse motor, 50 is a control unit, 55 is an engine starting sensor, 56 is a steering ratio characteristic specifying switch, 57 and 57゛ are steering ratio characteristic specifying units, 58 and 58° are steering ratio characteristic storage units, and 59 is a steering ratio characteristic specifying unit. 60 is a rear wheel steering angle calculating section, 61 is a pulse signal forming section, 62 is a driving section, 65 is a correction section, and 76 is a steering ratio changing mechanism. Figure 5

Claims (1)

[Claims] A front wheel steering mechanism that steers a front wheel in response to a steering operation in a vehicle, a rear wheel steering mechanism that steers a rear wheel in response to the steering of the front wheel, and a steering angle of the rear wheel relative to a steering angle of the front wheel. A steering ratio control means for changing a ratio change characteristic by manual operation, an engine start detection means for detecting the start of an engine installed in the vehicle, and an engine start detection means for detecting that the engine has started. When
The above-mentioned change characteristics controlled by the above-mentioned steering ratio control means,
Forcibly, when the running speed of the vehicle is relatively low, the steering state of the front wheels and the steering state of the rear wheels are forced to have the same phase relationship, thereby increasing the running stability of the vehicle. A four-wheel steering system for a vehicle, comprising: a specific steering ratio characteristic specifying means; and a steering ratio characteristic specifying means.